1. Field of the Invention
The invention relates in general to monopole antennas and in particular to monopole antennas for UHF/VHF radio signals.
2. Description of the Related Art
Embedded antennas, such as chip antennas and planar antennas, are widely applied in wireless communication devices. A conventional type is a ceramic chip antenna produced by LTCC (Low Temperature Co-fired Ceramic) technology. Conventional planar antennas such as microstrip antennas, printed antennas and planar Inverted F Antennas (PIFAs), are generally applied in GSM, DCS, UMTS, WLAN, and Bluetooth wireless equipment such as mobile phones and wireless LAN adapters.
Referring to FIG. 1, a conventional planar monopole antenna primarily comprises a substrate S, a ground G, a conductive element R and a cable W. The ground G and the conductive element R are formed on a surface S1 of the substrate S with the conductive element R longitudinal in direction Y.
The cable W, such as a coaxial cable, comprises a signal wire W1 enclosed by a ground wire W2. As shown in FIG. 1, the conductive element R comprises a feed end RF adjacent to the ground G. The feed end RF is connected to the signal wire W1, and the ground G is connected to the ground wire W2, respectively.
With regard to typical frequency range of Digital Video Broadcasting, the frequency coverage ratio of a conventional planar monopole antenna is usually less than 30%, adversely affecting communication efficiency. Moreover, it is not convenient to switch between VHF and UHF during usage due to bandwidth limitations of conventional planar monopole antennas.